1. Field of the Invention
This invention relates broadly to the field of convenience closures for full-open type can ends. More specifically, this invention relates to an improved rivet formation for attaching a gripping tab to an end panel of such a can end.
2. Description of the Prior Art
One form of self-opening can which is in wide use is the so called full-open can, in which a peripheral score, generally circular in configuration, is formed in the end panel at or adjacent to the periphery thereof to permit its complete removal. Full-open type cans are to be distinguished from those self opening cans which have a comparatively small removable section which, when opened, provide a comparatively small hole for dispensing the product. The latter type of can end is only appropriate for packaging soda, beer, or other liquids. Full-open type cans, on the other hand, are suitable for packaging solid products such as candy, nuts, meats, or ground coffee.
A conventional full-open type can end is depicted in FIGS. 1-3. Can end 10 conventionally includes an end panel 12 and an edge-curled peripheral flange 14 Which is adapted to be inter folded with an end flange of a can body. At or adjacent to the periphery of end panel 12 is a peripheral score 16 which is indented into the end panel 12 and defines a fixed can end portion 18 and a removable portion or panel 20. A gripping tab 22 is mounted to the end panel 12 by means of a rivet formation 24. The gripping tab 22 is positioned close enough to the peripheral score 16 so that when its inner end is rocked upwardly to cause its outer end to move downwardly and exert a downward force on the end panel 12 at or near the peripheral score 16, a portion of the end panel 12 is bent downwardly to initiate rupture of the peripheral score 16. Thereafter, an upward and backward pull on the gripping tab 22 by the user induces tearing of the metal in the peripheral score 16 on both sides of the area of initial rupture to complete detachment from the can of the removable portion or panel 20 of the end panel 12.
Typically, rivet formation 24 is formed out of the material of end panel 12 by die pressing or a similar process. Specifically, the rivet formation 24 includes a raised area 26 defined by an outer edge 28. Referring briefly to FIGS. 2 and 3, raised area 26 includes what is commonly termed a first operation bubble 30. First operating bubble 30 is ordinarily formed by a first die pressing operation in the end panel 12. Raised area 26 further includes a second operation bubble 32, which is formed in a second die press step which is performed on the first operation bubble 30, as may be seen in FIG. 3. The first and second operation bubbles 30, 32 are formed as concentric circles in the end panel 12. The second operation bubble 32 is subsequently formed into the flattened rivet head which secures the gripping tab 22 to the end panel 12.
To promote flexibility and to provide a hinge point for the tab 22 when it is lifted, a mustache score 34 is typically formed in the end panel 12, as is illustrated in FIG. 1. Mustache score 34 typically has an inner portion 36 defined on the raised area 26 of rivet formation 24, and at least one outer portion 38 defined on the outer surface of end panel 12. The inner portion 36 of mustache score 34 may be defined on the first operation bubble 30, and be curved about the radial inner periphery of the second operation bubble 32. The outer portions 38 of the mustache score 34 would typically be shaped so as to flare outwardly from the respective inner portions 36, and would typically end up substantially parallel to the peripheral score 16 at the outer most extent thereof.
Unfortunately, tearing would sometimes occur along the inner portion 36 of the mustache score 34 during opening. It is thought that such tearing initiates in the area of inner portion 36 which is adjacent to the second operation bubble 32, and that the tearing propagates along the mustache score 34 to the point where the mustache score 34 intersects with the outer edge 28 of the raised area 26 in rivet formation 24. The tearing would then continue to propagate radially outwardly along the outer edge 28 of the raised area 26, sometimes resulting in the failure of the can end 10 to open.
It is clear that there has existed a long and unfilled need in the prior art for an improved full-open type can end which is less susceptable to failure due to unwanted tearing during opening of.